This invention relates to a speed control apparatus for an automotive vehicle. More particularly, it relates to a speed control apparatus which can perform creep control at low vehicle speeds.
Cruise control devices which maintain the speed of a vehicle constant at high speeds have existed for many years. Recently, creep control devices for use at low vehicle speeds have been proposed. A creep control device is a device which maintains the speed of a vehicle constant when the vehicle is running at low speeds. Creep control is especially advantageous when travelling in congested traffic for long periods of time, when parking a vehicle in a garage, or when passing another vehicle along a narrow road. For example, Japanese Published Unexamined Patent Application No. 61-247525 discloses a creep control device in which a control unit adjusts the degree of opening of a throttle valve so as to maintain a constant, predetermined vehicle speed as long as the accelerator pedal is depressed. When the control unit is performing creep control, the vehicle speed is independent of the amount of depression of the accelerator pedal. When the driver removes his foot from the accelerator pedal, the control unit automatically applies the brakes and stops the vehicle. However, that apparatus has the disadvantage that the driver can not freely control the creep speed (the vehicle speed during creep control), which is set in advance.
Japanese Published Unexamined Patent Application No. 62-2155252 discloses a creep control apparatus in which the throttle valve and the brakes of a vehicle are both controlled by a control unit so as to maintain a predetermined creep speed. Creep control is performed only when the driver is not depressing either the accelerator pedal or the brake pedal. That apparatus likewise has the disadvantage that the creep speed is set in advance and can not be easily adjusted by the driver.